Electric heating apparatus and control



Aug- 24, 1948. J. w. HARRISON 2,447,649

ELECTRIC HEATING APPARATUS AND CONTROL Filed Sept. 24, 1942 2 Sheets-Sheet 1 F) Li O O O o 49 I I I Iii: l y IIIIlIIIIf/ I 4 5,4 31 n? 52 Q WITNESSES: INVENTOR 1%, .70/222 14! Harr'z'sarz.

A'I-TORNEY Aug. 24, 1948. J. w. HARRISON 2,447,649

ELECTRIC HEATING APPARATUS AND CONTROL Filed Sept. 24, 1942 2 Sheets-Sheet 2 INVENTOR J/m W Hair/23072.

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6. W68 fig ATTRNEY Patented Aug. 24, 1948 ELECTRIC HEATING APPARATUS AND CONTROL John W. Harrison, Mansfield, Ohio, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 24, 1942, Serial No. 459,482

4 Claims. 1

My invention relates to electric heating apparatus and controls therefor and particularly to an electrically-heated tool and adjustable means for controlling the temperature of said tool.

More specifically, my invention relates to an electrically-heated tool for heating explosive rivets which are used, for example, in airplane construction and in locations where it is difficult to use a bucking tool for driving standard rivets. However, the tool may be used for other purposes, such as soldering and the like.

In a tool for heatin explosive rivets, relatively high temperatures of between 900 F. and 1200 F. are required to fire the explosive contained in the rivets. Although the amount of heat necessary to fire each rivet is relatively small, it is desirable to heat a large mass of metal to the desired temperature so that continuous riveting may be accomplished without appreciable temperature change in the tool. A large mass of metal has sufficient heat storage capacity to effect this result and the amount of heat absorbed by the rivets is relatively small compared with the heat loss from the tool by radiation. It is, therefore, possible to control the temperature of the large mass of metal either by controlling the wattage input to the heating element or by thermostatically controlling the heating element. The wattage control has the advantage that the control device may be at a remote location from the hot parts of the tool, so that contact burning does not occur, while the thermostatic control has the advantage of compactness and somewhat closer control of the operating temperature of the device.

It is, therefore, an object of my invention, to provide an improved electrically-heated tool of the type wherein a large mass of metal is maintained at a substantially constant elevated tem perature.

It is another object of my invention to provide a novel wattage input control for an electricallyheated tool, and further to provide a readily accessible adjustment for the control.

It is a further object of my invention to provide an improved wattage control for an electrically-heated tool wherein the control is of the bimetal type.

It is still another object of my invention to provide a control for an electrically-heated tool which is at a remote location from the hot parts of the tool.

It is a further object of my invention to provide an improved thermostatic control for an electrically heated tool and further to provide a 2 bimetal temperature control element which is in metallic heat conducting relation with the part of the tool to which heat is directly applied.

It is still a further object of my invention to provide an improved thermostatic control for an electrically-heated tool and to provide for readily accessible adjustment of the thermostatic control.

It is also an important object of my invention to provide a novel electrically-heated tool and control therefor for riveting with explosive rivets.

These and other objects of my invention will become evident from the following description, taken in conjunction with the accompanying drawings, in which:

Figure 1 is a top view of an electrically-heated tool constructed in accordance with a preferred embodiment of my invention;

Fig. 2 is a side view, partially in section, of the tool shown in Fig. l, with a wattage control device also shown in section;

Fig. 3 is a wiring diagram for the tool and control shown in Figs. 1 and 2;

Fig. 4 is a side view, partially in section, of a second embodiment of my invention;

Fig. 5 is an enlarged top View of the thermostat used in Fig. 4, showing the electrical connections; and

Fig. 6 is an enlarged sectional view of the thermostat used in Fig. 4.

Referring specifically to Figures 1, 2 and 3 of the drawings for a detailed description of the first embodiment of my invention, numeral ll designates generally an electrically-heated tool for explosive riveting. The tool ll includes a handle l2, a tube 13 containing an electric cable I I, a junction box 15 attached to tube l3 and a head l6 formed of a large mass of metal. An electrical heating element ll, preferably of the rod type, is embedded in the head 16 and is provided with terminals l8 which support the head Hi from the junction box 15. A working tip I9, having female threads 2| therein, is attached to male threads 22 on the head l6, so that intimate metallic engagement is effected between the two and the temperature of the head I6 and tip 2| will be substantially the same. A second handle 23 and a heat shield 24 are also supported from the junction box 15. The electric cable M is provided with an electrical connecting plug 25.

As best shown in Fig. 2, an adjustable wattage control device, generally indicated at 26, is electrically connected to the tool II by an electrical socket 21 which is engaged by plug 25 and is connected to a source of power (not shown) by an electrical plug 28. The adjustable wattage control device 26 comprises a metal casing 29 enclosing a snap-acting bimetal element 3|, for example, of the Spencer disc type, a heater 3'3 in heat exchange relation with the bimetal element 3! and a second metal casing 33 enclosing the bimetal element 3! and heater 32. The casing 33 is supported on insulating studs 34 and an adjusting knob 35, accessible from the top of the casing 29, is attached to a threaded shaft 36. The threaded shaft 36 extends through both the casings 29 and 33 and varies the bias of the bimetal element 3|, thereby changing the temperature at which it snaps 'froincrie position to the other. As the adjusting knob 35' and shaft 36 are rotated in one direction, the end of the threaded shaft depresses the center of the bi metal element 3! so that a higher temperature is required to snap it to the open position. Therefore, the input to the heating element I! is increases and the head at an up as are maim tained at a higher temperature. Asthe'knob 35 and shaft 36 are rotated in the opposite 'direction; the center of the 'binietal element 3! is raised, and the head I6 and tip i9 operate at lower temperature. Ah electrical cord 31 connects socket 2'! to the Wattage control device 2i: and an electrical cord 38 connects the wattage control device 26 with plug 28.

best shown in Fig. 3, the heating element ill is supplied with electrical energy through con- (meters 39 and '40, theeon'auctor 39 being connected to a fiiied (zol'ltatit 4'! Of the wattage control device 26 and the 'con'duetor Ml connecting with one side of the source of power. The wattage control device is provided with three additional fined contacts 2 2, 3 and M. The electric heater 32 is connected betweencohtacts 42 and d3 a conductor 45 connects the contact Ml to the other side of the source of power. The snap-actingbimetal element is provided with a plurality of moving contacts 56 and 4? each of which bridges a pair of the fixed cont'acts, namely, contacts 4! and 42 and contacts 53- and tirespectively. Agroiind or ne'utral conductr 48 extends between the head it and the casing- 33 "and 'a'se'c'ohd heutral conductor G9 extends be tween the casing 33 and ground, thus preventing any possibility ofa shock from head H3 or casing or 29. y Y

As'shown in Fig. 3, the workin'g tip i9 ispre's'sed a airi st the head of a rivet 50 containing an ex pl'osive charge 5! inits shank. When the heat from the tip-l9 'e'x'plodes the charge 5!, the "shankof the rivet spreads and rivets two pieces (if metal'ez'together. Y I

operation, where thetool H and wattage control device 2'6- areconn'ected tda'source of power, the bimetal element 3| starts a cycle in the position shown in Fig. 3 with :rnovahlev contacts 46 and '41 "bridging fixed contacts 4] t? and 43, 44, respectively. 'Current, therefore, flows through conductor 49, heating element lland back to contact 4H through conduc'tortfi. Curr'ent then flows across i'novable contact 46 toterminal 42 through thermostat heater 32 to "fixed contact 43, across movable contact 61 to fixed contact 44 and then back to the sourceof power through conductor 45 Both the main heater H and thermostat heater 32 are energized, and assuming that the head 16 and tip ['9 have already been "elevated to hearthe desired riveting ternperature, heat will be supplied to them in suffi Hi nt quantitie's to overcome-the "relativelyda-rge 'heatradiation lossesand the relatively small heat 4 losses due to contact of the tip I9 with rivets 55. As the thermostat heater receives energy, it heats the bimetal element 3| to a temperature depending on the setting of knob 35. When uch a temperature is attained, the bimetal element snaps to the position shown in dotted lines in Fig. 3 and opens the contacts, thereby deenergizing both the thermostat heater 32 and main heater IT. The bimetal element then co-ols by radiation until it reaches a temperature where it again snaps to the position shown in Fig. 2, thus again energizing the thermostat heater 32 and the main heater H. The wattage input to the heater H is, therefore, constant for a particular setting of the knob '35 and is s'ufiic'ient to overcome the heat losses due to radiation and riveting. Since the radiation loss is the major heat loss and since the head it and tip i9 have large heat storage capacity, a constant wattage control is satisfactory to maintain a substantially constant temperature of the head [6 and tip l9.

It is, therefore, apparent that I have provided a novel electrically heated tool and wattage control therefor wherein the temperature of the heated parts of the tool are maintainedat a'sub- 'stantially constant high temperatureand wherein the controlling device is in a remote location where its parts are not affected by the high temperature portions of the tool. Furthermore, the device is self-compensating for a fairly wide range of voltage variations because the thermostat heater and main heater are connected in series and voltage changes affect the heat generated by both heaters to the same degree.

Referring now to Figs. 4 to 6, inclusive, for a detailed description of the second embodimentof my invention, numeral 53 designates generall'y'an electrically heated tool having handles 54 and 55, a heat shield 56, a junction box 51, a head 58 and a working tip 59, assembled much in the same manner as the tool shown in Figs. 1 to 3, inclusive.

In this embodiment of my invention, an adju'stable thermostat, generally indicated at 6| is associated with the head 58 to control the temperature thereof. The thermostat 6| comprises acreep-acting bimetal element-62 held'in metallic contact with the head 53 by insulating studs/63. Also mounted on the studs '63 is a spring arm 6 1 carrying a movable contact 65 and having a leg 66 extending toward the free end of the bimetal element fizfor engagement therewith. A lowerspring arm El is also mounted on the studs "63 and carries an adjustable contact 68. A casing 69 encloses the thermostat BI and a threaded shaft 'HJ extendsthroughthe casing 69, the junction box 5'! and through'a passage H in the handle 54. An adjusting knob 12 is'provided on the'e'nd ofthe'shaft min a 'readilya'cces'sible position at theback of handle Asthe threaded shaft i8 is turned, its'ehd bears on the springa'rm 67 ahd h'an'ges the lilos'itio'il "pe'rature or the headtiB and tip 59. When the knob '12 and shaft H are turned in theepposite direction, the arm 61 raises and the-temperature of head 58"a'nd tip 59 is increased.

A'r;tnductor 13 connects one terminal 15"01' a heating element 16 to a source of power (not shown). A conductor M is connected to the source of power and to an ear H on the upper spring arm 64 which carries one contact 65. A conductor 78 connects a second terminal E9 of the heating element '15 to an ear 8| of the lower spring arm 6'! which carries the contact 63. As shown in Figs. 4 and 6, the head 53 is hot and the bimetal element 62 has flexed to the position shown to open the contacts 65 and 68. As the head 58 and, therefore, the bimetal element 62 cool, the bimetal element flexes toward the head 58 and lowers the spring arm 64 and contact 65 until contacts 65 and 68 engage and energize the heater 16 through the circuit just described. Due to the fact that the bimetal element 62 is in direct metallic engagement with the head 58, very close control of the temperature of the head 58 and working tip 59 is efiected.

From the foregoing it will be apparent that I have provided an electrically-heated tool which is readily adjustable to various operating temperatures and a thermostatic control which maintains the desired temperature within very narrow limits.

I do not wish to be restricted to the specific structural details, circuit connections or relations of parts hereinbefore set forth, as further modifications thereof may be effected without departing from the spirit and scope of my invention. I desire, therefore, that only such limitations shall be imposed thereon as are indicated in the appended claims.

I claim as my invention:

1. In an electrically-heated tool for heating metallic materials, the combination of an elongated working head comprising a heavy mass of metal for storing large quantities of heat, an electric heating element for heating said working head to a substantially uniform temperature throughout, said working head having a front end portion for applying heat to said material and a cup-shaped supporting member at the rear end of the head, an electrical circuit connecting said heating element to a source of power and a pair of terminals in said electric circuit; a bimetal thermostat control element in intimate contact with the rear portion of said working head and located between the working head and said supporting member, said thermostatic element operating, with temperature variations, to open and close said pair of terminals in the electric circuit to control the temperature of said working head; a handle having a portion extending in substantial alignment with said working head, said handle having a finger grip at the rear portion and a cup-shaped supporting member at the front end; said first-mentioned cup-shaped member being connected with the second-mentioned cup-shaped member by telescoping the two members together, and means to lock the members in telescoped relation, where by said elongated working head is assembled in working relation with said handle, with a heat insulating chamber therebetween to stop excessive heat flow from the working head to the handle.

2. In an electrically heated tool for heating metallic materials, the combination of an elongated working head comprising a heavy mass of metal for storing large quantities of heat, an electric heating element for heating said working head to a substantially uniform temperature throughout, said working head having a front end portion for applying heat to said material and a" cup-shaped supporting member at the rear end of the head, and terminals for said electric heating element inside the cup-shaped supporting member; a handle having a portion extending in substantial alignment with said working head, said handle having a finger grip at the rear portion and a cup-shaped supporting member at the front end; said first-mentioned cup-shaped member being connected with the second-mentioned cupshaped member by telescoping the two members together, and means tolock the members in telescoped relation, and an electric circuit extending through one of said cup-shaped members, connected to saidterminals and to a source of power, whereby said working head and said handle are connected in working relation, with the heat conducting partsof said working head made discontinuous at the heat radiating chamber to stop ex-- cessive heat flow from the working head to the: handle.

3. In an electrically-heated tool for heating: metallic materials, the combination of an elongated working head comprising a heavy mass of metal for storing large quantities of heat, an. electric heating element for heating said working: head to a substantially uniform temperature throughout, said working head having a front end portion for applying heat to said material and a. cup-shaped supporting member at the rear end of the head, control means for maintaining saidi working head at substantially constant temper:-- ature comprising a bimetal thermostatic elemenit attached to the rear end portion of said working head and contact means arranged to be opened and closed by said thermostat element, a casingv located between said working head and the cup-- shaped supporting member, enclosing said ther-- mostat and contacts and means connecting saidl heating element and contacts in series and to two electric terminals, at least one of which is located in said cup-shaped supporting member, a handle: having a portion extending in substantial alignment with said working head, said handle having a finger grip at the rear portion and a cup-shaped supporting member at the front end; said firstmentioned cup-shaped member being connected with the second-mentioned cup-shaped member by telescoping the two members together and means to lock the members in telescoped relation; means extending through said handle and said cup-shaped support for adjusting the position of the thermostatic element, and an electric circuit extending through one of said cup-shaped. members, connected to said terminals and to av source of power, whereby said working head and said handle are connected in working relation, with the heat conducting parts of said working: head made discontinuous at the heat radiating: chamber to stop excessive heat flow from the working head to the handle.

4. In an electrically-heated tool for heating metallic materials, the combination of an elongated working head comprising a heavy mass of metal for storing large quantities of heat, an electric heating element for heating said Working head to a substantially uniform temperature throughout, leads for said heating element projecting to the rear of and in axial alignment with said working head, said working head having a front end portion for applying heat to said material and a cup-shaped supporting member mounted on said leads at the rear end of the head and terminals for said leads inside the cup-shaped supporting member, a handle having a portion ex- 7 tending in substantial alignment. with said work-- ing head, said handle having a finger grip at the rear portion and a cup-shaped supporting. memher at the front end; said first-mentioned cupshaped member being connected with the secondmentioned cup-shaped member by telescoping the two members together, and means to lock the members in telescoped relation, and an electrical circuit connecting said terminals to a source of power, whereby said elongated. working head is assembled in Working relation with said handle with the working head and heating element leads terminating at a heat insulating chamber to stop excessive heat flow from the workinghead to the handle.

JOHN W. HARRISON.

REFERENCES CITED The following references are of record in the file of this patent:

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